Ink for oil-based ball pen

ABSTRACT

Provided is an oil based ink for a ball-point pen comprising at least an alcohol-soluble dye, carbon black, a resin and an organic solvent, wherein the carbon black described above has a DBP oil absorption of 80 cc/100 g or less. The carbon black has preferably a particle diameter of 30 mμ or less and a content of 1 to 15 mass % based on the total amount of the ink.

TECHNICAL FIELD

[0001] 1. Field of the Invention

[0002] The present invention relates to an oil based ink for aball-point pen, specifically to an oil based ink for a ball-point pen inwhich an alcohol-soluble dye is used in combination with carbon black asa coloring material and which is excellent in stability with the passageof time.

[0003] 1. Background Art

[0004] An oil based ink for a ball-point pen in which an oil-soluble dyeis used in combination with carbon black is disclosed in Japanese PatentApplication Laid-Open No. Hei 11-293174.

[0005] However, carbon black is no more than being described in theexamples in this official gazette, and it is understood as if carbonblacks of all grades can be used. In many cases, however, when carbonblacks are used for an oil based ink for a ball-point pen, caused arethe problems in that the ink is short of stability with the passage oftime and that when the ball-point pen is used for a long time, the inkdischarge amount is reduced to a large extent or on the contrary, itgrows large in a certain case.

[0006] On the other hand, the advantage that an alcohol-soluble dye isused in combination with carbon black resides in the point that problemswhich are difficult to overcome by themselves alone can be solved bymaking best use of the merits thereof each other. For example, if onlyan alcohol-soluble dye is used, drawn lines are a little inferior infastness such that the lines drawn on paper are eluted or decolored byalcohol base solvents (alcohol resistance) or oxidation-reduction agents(chemical resistance) or that when exposed to sunlight, they are fadedor decolored in a short time (light fastness). Accordingly, in order toobtain good drawn line fastness, particularly good light resistance, ametal-containing dye containing chromium, which is a heavy metal, in adye skeleton has to be used in a large amount, so that likely to becaused is an environmental problem such as leaking of chromium, though atrace amount, into the environment due to incineration treatment.

[0007] Further, a Nigrosine base dye is available as a black dye havingvery high fastness, but this dye has a peculiar odor, and thereforethere is a problem in that it is unpleasantly felt for some users inwriting.

[0008] In contrast with this, when only carbon black is added to an inkin an amount sufficient for obtaining a practically satisfactory drawnline density, it is difficult in practice to industrially produce acarbon black dispersion having a high concentration. The ink is inferiorin stability with the passage of time and falls into an unwritable statein a very short period of time, and it has a problem in cost. Further,when priority is put on stability with the passage of time, asufficiently large amount of carbon black can not be contained in anink, so that the drawn lines are light and the ink does not standpractical use.

[0009] In light of the problems described above, the present inventionis intended for solving them, and an object thereof is to provide an oilbased ink for a ball-point pen which is excellent in stability with thepassage of time in a combined use system of an alcohol-soluble dye andcarbon black and which has less change in a discharge amount when aball-point pen is used for a long time.

DISCLOSURE OF THE INVENTION

[0010] Intensive researches repeated by the present inventors in orderto solve the problems described above have resulted in finding that anink is excellent in stability with the passage of time when carbon blackused has a DBP oil absorption of 80 cc/100 g or less and that a changein the discharge amount in using a ball-point pen for a long time issmaller when it has a particle diameter of 30 mμ or less, and thus thepresent invention has come to be completed. Further, it has been foundthat if carbon black contained in the ink has a content of 1 to 15 mass%, the sufficiently high fastness is obtained and the stability with thepassage of time is much more improved and that a change in the dischargeamount caused when the ball-point pen is used for a long time is less.

[0011] That is, the present invention comprises:

[0012] (1) an oil based ink for a ball-point pen comprising at least analcohol-soluble dye, carbon black, a resin and an organic solvent,wherein the carbon black described above has a DBP oil absorption of 80cc/100 g or less,

[0013] (2) the oil based ink for a ball-point pen as described in theabove item (1), wherein the carbon black has a particle diameter of 30mμ or less, and

[0014] (3) the oil based ink for a ball-point pen as described in theabove item (1) or (2), wherein the carbon black has a content of 1 to 15mass % based on the total amount of the ink.

[0015] The oil based ink for a ball-point pen according to the presentinvention can provide an oil based ink composition for a ball-point penwhich is excellent in stability with the passage of time and which hasless change in a discharge amount in use of a ball-point pen byregulating the characteristics of carbon black used.

BEST MODE FOR CARRYING OUT THE INVENTION

[0016] The embodiment of the present invention shall be explained belowin details.

[0017] The DBP oil absorption of carbon black described in the presentinvention means a volume (cc) of dibutyl phthalate (DBP) which isadsorbed on 100 g of carbon black, and it shows primarily a structure(three-dimensional state of an aggregate of primary particles) of carbonblack.

[0018] The particle diameter of carbon black means an average value ofdiameters of primary particles of carbon black which is measured bymagnifying under an electron microscope.

[0019] In the present invention, it is not sure why the excellentstability with the passage of time is obtained when carbon black havinga DBP oil absorption of 80 cc/100 g or less, preferably 80 cc/100 g to40 cc/100 g is used unlike other carbon blacks. However, carbon blackhaving a DBP oil absorption exceeding 80 cc/100 g exhibits a higherviscosity when dispersed because of a larger structure thereof, and arequired amount of a binder grows larger as well. This is considered tobe a factor for deteriorating the stability with the passage of time.

[0020] It is not certain either why when carbon black having a particlediameter of 30 mμ or less is used, a change in the discharge amountcaused when a ball-point pen is used for a long time is small. However,when hard particles such as carbon black are present in an ink, theywork as if they are abrasive particles in a tip in writing, whereby thetip is abraded in an inside thereof, and the respective parts cause adimensional change to a large extent as compared with the original. Thiscauses a change such as a reduction or an increase in the dischargeamount in a certain case, and it is considered that when carbon blackhas a particle diameter of 30 mμ or less, it is sufficiently small as anabrasive particle and therefore provides less abrasion, so that a largedimensional change is not caused. As a result, it is considered that alarge change in the discharge amount is not observed even when theball-point pen is used for a long time. Further, selection of carbonblack having a BET specific surface area of 100 m²/g or less among thesecarbon blacks makes it possible to readily control a viscosity of theink.

[0021] The alcohol-soluble dye used in the present invention includesAizen Spilon Yellow C-2 GH, Aizen Spilon Yellow C-GNH, Aizen Spilon RedC-GH, Aizen Spilon Red C-BH, Aizen Spilon Violet C-RH, Aizen Spilon BlueC-RH, Aizen S.B.N. Blue 701, S. B. N. Yellow 530, S. B. N. Violet 510,Valifast Yellow 1110, Valifast Yellow 3150, Valifast Violet 1701,Valifast Violet 1702 and Valifast Red 1360.

[0022] These alcohol-soluble dyes each may be used alone or in a mixtureof two or more kinds thereof. These alcohol-soluble dyes are addedpreferably in a range of 5 to 50 mass %, preferably 15 to 40 mass %based on the total mass of the ink composition. If the blending amountis less than 5 mass %, the drawn line density becomes light. On theother hand, if it exceeds 50 mass %, an adverse effect is exerted on theother blended components.

[0023] Carbon black used for the ink composition of the presentinvention includes, for example, pigments such as Reagal 400R and MogulL manufactured by Cabot Co., Ltd., Printex 25, Printex 35, Printex 45,Printex 55, Printex 75, Printex 85 and Special Black 550 manufactured byDegussa AG and #33, #44, #45, #52, #45L, #50, #900, #970, #1000, #2300,#2350, MA7, MA8, MA11 and MCF88 manufactured by Mitsubishi ChemicalCorporation.

[0024] A blending amount of the coloring material of thesealcohol-soluble dye and carbon black falls in a range of 6 to 65 mass %,preferably 20 to 50 mass % in total based on the total mass of the inkcomposition. In this case, a blending amount of carbon black falls in arange of 1 to 15 mass %, preferably 5 to 10 mass % based on the totalmass of the ink composition. If a blending amount of the coloringmaterial is less than 6 mass %, the density of drawn lines in writing islight and therefore is not practical. On the other hand, if it exceeds65 mass %, a reduction in a solvent caused by volatilization gives riseto a large problem in the stability with the passage of time because theviscosity of the ink rises and the solubility of the coloring materialbecomes short. Further, if a blending amount of carbon black is lessthan 1 mass %, the drawn lines are short of fastness, and it isparticularly difficult to visually observe the drawn lines remaining inan alcohol resistance test. On the other hand, if it exceeds 15 mass %,a pseudo-plasticity of the ink is strengthened, and followability of theink in quickly writing is deteriorated or an adverse effect is exertedon the stability with the passage of time.

[0025] An organic solvent is used for the ink composition of the presentinvention in order to dissolve or disperse the coloring materialdescribed above. In this case, used as the organic solvent is an organicsolvent which is used for a conventional oil based ink for a ball-pointpen, that is, an organic solvent which dissolves or disperses thecoloring material described above and which has a relatively highboiling point. Such solvent includes, for example, benzyl alcohol,phenoxyethanol, carbitols and cellosolves. They may be used alone or ina mixture of two or more kinds thereof, and a blending amount thereoffalls preferably in a range of 20 to 70 mass % based on the total amountof the ink composition of the present invention. In this case, if it is20 mass % or less, it is not preferred in terms of a solubility of thecoloring material and others. On the other hand, if it is 70 mass % ormore, it is not preferred either in terms of a shortage of the colorantresulting in insufficient density of the drawn lines.

[0026] Further, a resin may be added as a dispersant or aviscosity-controlling agent to the ink composition of the presentinvention, and capable of being given as the examples thereof are resinsused for conventional oil based ink compositions for a ball-point pen,for example, ketone resins, acetophenone resins, sulfamide resins,maleic acid resins, butyral resins, ester gums, xylene resins, alkydresins, phenol resins, rosin resins, polyvinylpyrrolidone resins andmodified resins thereof. These resins may be used alone or in a mixtureof two or more kinds thereof.

[0027] These resins have a content of 5 to 30 mass % based on the totalamount of the ink composition. In this case, if it is 5 mass % or less,it is not preferred in that the viscosity of a minimum required limit isnot obtained. On the other hand, if it is 30 mass % or more, it is notpreferred either in that the resulting viscosity becomes too high.Capable of being added, if necessary, to the ink composition of thepresent invention are, in addition to the essential components describedabove, other additives used for a conventional oil based ink for aball-point pen, for examples, fatty acids, phosphoric acid ester baselubricants, surfactants, rust preventives, antioxidants and lubricatingoils.

EXAMPLES

[0028] The present invention shall be explained below in further detailswith reference to examples, comparative examples and test examples, butthe present invention shall by no means be restricted by these examples.

Examples 1 to 4 and Comparative Examples 1 to 4

[0029] Produced by the following production process were oil-based inksfor a ball-point pen comprising in combination respective components ofalcohol-soluble dyes, various carbon blacks, solvents, resins andlubricants. In producing the inks, carbon black was first dispersedusing a butyral resin as a dispersant by a usually well known method,for example, by means of a ball mill or a three roll mill andtransferred into a vessel equipped with a reflux condenser and astirrer, and then the other components were added thereto and stirred at60° C. for 10 hours. Impurities were removed by pressure filtration toprepare oil-based inks for a ball-point pen of Examples 1 to 4 andComparative Examples 1 to 4 shown in Table 1. Numerical values in thecompositions shown in Table 1 show mass parts. TABLE 1 DBP oil Particleabsorption diameter Example Comparative Example Raw material name(cc/100 g) (mμ) 1 2 3 4 1 2 3 4 Colorant Carbon Printex 25*¹ 46 56 10.0black Printex 45*¹ 52 26 8.0 25.0 #33*² 76 28 13.0 Carbon 125 35 10.0black LT*¹ MA100*² 100 22 8.0 Printex 95*¹ 100 15 13.0 Alcohol- AizenSpilon 15.0 16.0 10.0 10.0 15.0 16.0 10.0 20.0 soluble Violet C-RH*³ dyeAizen Spilon 6.0 4.0 6.0 6.0 4.0 Yellow C-2GH*³ Aizen Spilon 5.0 5.010.0 Yellow C-GNH*³ Example Comparative Example Raw material name 1 2 34 1 2 3 4 Solvent Benzyl alcohol 10.5 6.0 10.0 6.0 4.5 12.0 15.0 10.52-Phenoxyethanol 45.0 45.5 42.5 27.0 45.0 45.5 42.5 40.0 Tripropyleneglycol 6.0 5.0 10.0 6.0 n-butyl ether Resin Denka Butyral 2.0 2.0 4.52.0 2.0 #2000-L*⁵ S-leck B BL-1*⁶ 2.0 2.0 Synthetic Resin SK*⁴ 8.0 11.010.0 8.0 8.0 11.0 10.0 16.0 PVP K90*⁷ 0.5 0.5 0.5 0.5 0.5 0.5 PVP K120*⁷0.5 0.5 Lubricant Oleic acid 3.0 3.0 3.0 3.0 3.0 3.0 Total 100.0 100.0100.0 100.0 100.0 100.0 100.0 100.0

[0030] The respective oil-based inks for a ball-point pen prepared bythe process described above were filled into a refill having apolypropylene tube and a stainless tip (a ball is made of hard metal andhas a diameter of 0.7 mm), and this was then incorporated into acommercially available barrel of SA-R manufactured by Mitsubishi PencilKabushiki Kaisha and finished into oil-based ball-point pens. Theserefills or oil-based ball-point pens were used to carry out thefollowing tests of stability with the passage of time and the like.

[0031] 1) Test of Stability with the Passage of Time

[0032] The fifteen refills described above per each ink were stored for3 months in a constant temperature and constant humidity bath of 50° C.and 80% RH, and each 5 refills were taken out every month and left tocool down to room temperature. Then, they were used for writing spiralswith a hand to inspect a writing property according to the followingcriteria:

[0033] ⊚: capable of writing as well as before the test

[0034] ◯: a little change observed as compared with before the test

[0035] Δ: starving is caused

[0036] □: starving is heavy

[0037] ×: incapable of writing

[0038] 2) Change in Discharge Amount

[0039] The five oil-based ball-point pens were used for writing up to1000 m under the conditions of a load of 200 g, a writing angle of 70°and a writing speed of 4.5 m/minute by means of a writing test machinewhile measuring the discharge amount for every 100 m, and a dischargeamount of the ink in 0 to 100 m was compared with a discharge amount ofthe ink in 900 to 1000 m to judge the performance by the differencethereof:

[0040] ⊚: difference is ±2 mg or less

[0041] ◯: difference is ±5 mg or less

[0042] Δ: difference is +10 mg or less

[0043] □: difference exceeds ±10 mg

[0044] ×: incapable of writing in 900 to 1000 m

[0045] 3) Fastness of Drawn Lines

[0046] A piece of paper cut out from the paper having the drawn linesobtained in 2) described above was immersed in ethanol for a whole dayand night and taken out, and it was dried and then visually observed astate of the drawn lines:

[0047] ◯: firm drawn lines can be observed

[0048] Δ: faint drawn lines remain

[0049] ×: drawn lines flow out and can not be observed

[0050] The evaluation results thereof are shown in Table 2. TABLE 2 Testof stability with the passage Change in Fastness of time discharge ofdrawn 1 M 2 M 3 M amount lines Example 1 ⊚ ⊚ ∘ Δ ⊚ 2 ⊚ ⊚ ⊚ ⊚ ⊚ 3 ⊚ ⊚ ⊚ ∘⊚ 4 ⊚ ∘ Δ Δ ⊚ Comparative 1 ⊚ ∘ x □ ⊚ Example 2 Δ □ x □ ⊚ 3 ∘ Δ □ □ ⊚ 4⊚ ⊚ ⊚ ⊚ x

INDUSTRIAL APPLICABILITY

[0051] The oil-based ink for a ball-point pen according to the presentinvention is excellent in stability with the passage of time and suitedas an oil-based ink for a ball-point pen having less change in thedischarge amount when a ball-point pen is used for a long time.

What is claimed is:
 1. An oil based ink for a ball-point pen comprisingat least an alcohol-soluble dye, carbon black, a resin and an organicsolvent, wherein particularly the carbon black has a DBP oil absorptionof 80 cc/100 g or less.
 2. The oil based ink for a ball-point pen asdescribed in claim 1, wherein the carbon black has a particle diameterof 30 mμ or less.
 3. The oil based ink for a ball-point pen as describedin claim 1 or 2, wherein the carbon black has a content of 1 to 15% bymass based on the total amount of the ink.